In a process of manufacturing a semiconductor device, various kinds of gas processing are performed on a semiconductor wafer (hereinafter referred to as a wafer) as a substrate. There is a case that this gas processing is performed by mixing various kinds of gases and supplying a mixture gas onto the wafer. In that case, a common gas flow path, for the plurality of gases supplied from the upstream side, mixes each gas while flowing therein and is installed in a processing apparatus.
However, since the gases are not sufficiently mixed in the common gas flow path, the concentration distribution of the gases may be biased in the downstream side of the common gas flow path. As a result, there is a concern that the uniformity of processing of various portions in the plane of the wafer is not sufficiently increased due to different concentration distributions of the gases in the various portions of the wafer.
It is conceivable to detect a specific flow rate ratio of each gas at which a deviation of the concentration distribution can be suppressed and to process the wafer with the detected specific flow rate ratio. However, in order to increase the degree of freedom of wafer processing, it is required to set a wide range of flow rate ratios, without being limited to such a specific flow rate ratio. Further, it is conceivable to install a rectifying member in the common gas flow path so that, for example, the gases form a swirl flow and are efficiently mixed. However, since a space in which the processing apparatus can be installed is limited and the size of the common gas flow path is also limited, such a rectifying member cannot be installed.
For example, there has been proposed a film forming apparatus for forming a metal oxide thin film on a wafer. In this film forming apparatus, a vertically elongated gas mixing part is installed above a gas shower head, a precursor gas and a dilution gas supplied from an upper side of the gas mixing part respectively are mixed with each other while flowing downward within a space in the gas mixing part and are further mixed with an oxidizing gas supplied into the gas shower head. With such a configuration, it may be said that the gases can be mixed while suppressing the size of the mixing part. However, there is a need for a technique for further suppressing the size of the apparatus and mixing the gases with higher reliability. There has also been proposed an apparatus for supplying and dispersing a processing gas on a substrate by means of a manifold. However, this proposed technique does not involve solving the above problem.